Development of aerobic granular sludge
(2013) 1st Meeting of the Belgian Interdisciplinary Biofilm Research — Location: Louvain-la-Neuve (20.December.2013)
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- (en) The discharge of untreated wastewaters in the environment is responsible of the rapid degradation of aquatic ecosystems. The current leading technology to treat important volumes of wastewater is the activated sludge process, where the dissolved pollution is degraded by free floating microbial consortia called “flocs”. The major drawback of these loose aggregates is their low settling velocity, which imposes large clarifiers to separate them from treated water. An emerging technology aims to improve this process by selecting consortia that form aerobic granules. As dense aggregates, they settle significantly faster than flocs, which may reduce both capital and operational cost of treatment plants. However, conditions to obtain, and maintain, granules are still challenging, and the role of constituting microorganisms on both granule formation and pollution removal is largely unknown. This research aims to develop efficient batch reactors that can promote granulation from different wastewater sources. The performances of the reactors are recorded and the dynamics of microbial communities are assessed. The expected outcomes of the project are both fundamental and applied, as it will give a better understanding of aerobic granulation and it will be the first step towards the implementation of this technology in the Walloon Region. Stable granulation has already been achieved with artificial wastewater. Feeding is to be done from the bottom of the reactor, within the granular sludge bed. Cycles include a short settling time to select dense granules and a long feeding phase followed by an aeration phase to favor accumulating organisms. The major problem is the development of filamentous bacteria on the periphery of the granules. At least two different species are involved, including Microthrix sp., a bacterium that causes foaming in activated sludge plant. The bacterial composition of granules is very different between reactors, which seems to confirm that there is not a single microbial community that leads to granules. Several genera have been identified, including the Rhodocyclaceae genera Zoogloea, Thauera and Dechloromonas. The effect of granule density on bacterial composition has been assessed with Denaturing Gradient Gel Electrophoresis (DGGE) technique. Three reactors with different operating conditions were tested. Granules were separated on a sucrose gradient and collected in three fractions. So far, DGGE profiles of granules have not clustered in sucrose fractions. A preliminary experiment to assess the effect of granular size has been conducted. Granules were separated in 3 classes. The largest granules are clustered, while medium and small-sized granules are not. Complementary work is ongoing to confirm this trend.
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Henriet, O., Meunier, C., Henry, P., & Mahillon, J. (2013). Development of aerobic granular sludge. 1st Meeting of the Belgian Interdisciplinary Biofilm Research, Louvain-la-Neuve. https://hdl.handle.net/2078.5/193239